1. Technical Field of the Invention
The present invention relates to the cosmetic administration of compounds that increase the level of glutathione (GSH) in the melanocytes of the hair follicle for treating canities.
2. Description of Background and/or Related and/or Prior Art
The hair follicle is a tubular invagination of the epidermis which extends to the deep layers of the dermis. The bottom part, or hair bulb, itself comprises an invagination in which the dermal papilla is located. The bottom part of the bulb is a cell proliferation zone where the precursors of the keratinized cells making up the hair are found. The ascending cells derived from these precursors become gradually keratinized in the top part of the bulb, and this group of keratinized cells will form the hair shaft.
The color of head hair and of body hair depends in particular on the presence, in variable quantities and ratios, of two groups of melanins: eumelanins (brown and black pigments) and pheomelanins (red and yellow pigments). The pigmentation of head hair and of body hair requires the presence of melanocytes in the bulb of the hair follicle. These melanocytes are in an active state, that is to say that they synthesize melanins. These pigments are transmitted to the keratinocytes intended to form the hair shaft, which will result in the growth of a pigmented head hair or body hair. This structure is called hereinafter “follicular unit of pigmentation”.
In mammals, melanogenesis involves at least three enzymes: tyrosinase, DOPAchrome tautomerase (TRP-2, for Tyrosinase Related Protein 2) and DHICAoxidase (TRP-1, for Tyrosinase Related Protein 1).
Tyrosinase is the enzyme which initiates the biosynthesis of melanins. It is also described as being the limiting enzyme of melanogenesis.
TRP-2 catalyzes the tautomerization of DOPAchrome to 5,6-dihydroxyindole-2-carboxylic acid (DHICA). In the absence of TRP-2, DOPAchrome undergoes spontaneous decarboxylation to form 5,6-dihydroxyindole (DHI).
DHICA and DHI are both precursors of pigments, TRP-1 oxidizes DHICA molecules to form derivatives of quinones (Pawelek J. M. and Chakraborty A. K., The Enzymology of Melanogenesis. In: Nordlund J. J., Boissy R. E., Hearing V. J., King R. A., Ortonne J. P. The Pigmentary System: Physiology and Pathophysiology, New York: Oxford University Press; 1998. p. 391-400).
The three enzymes, tyrosinase, TRP-2 and TRP-1, appear to be specifically involved in melanogenesis. Furthermore, the activity of these three enzymes has been described as being necessary for the maximum activity of biosynthesis of eumelanins.
Head hair and body hair undergo a cycle. This cycle comprises a growth phase (anagen phase), a degenerative phase (catagen phase) and a resting phase (telogen phase) after which a new anagen phase will develop. Because of this hair cycle, and unlike the epidermal pigmentation unit, the follicular unit of pigmentation-must also be cyclically renewed.
Canities (natural graying of the hair) is linked to a specific and gradual depletion of the melanocytes of the hair which affects both the melanocytes of the hair bulb and the precursor cells for melanocytes (Commo et al., Br. J. Dermatol., 2004; 150: 435-443). Other cell types present in the hair follicles are not affected. Furthermore, this depletion of melanocytes is not observed in the epidermis. The cause of this gradual and specific depletion of melanocytes and precursors of melanocytes in the hair follicle has so far not been identified.
It therefore appears to be necessary to combat the disappearance of the melanocytes of the human hair follicles, a process which affects both the active melanocytes of the bulbs and the quiescent melanocytes of the top region of the hair follicles, in order to combat canities.
The assignee hereof has already described a means for combating graying of the hair by action on the enzyme TRP-2 (WO 03/103568).